<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 40px;
            height: 40px;
            line-height: 40px;
            border: 1px solid green;
            /* 内边距(文字到边框的距离) */
            padding-left: 40px;
        }
        .inner1{
            width: 0px;
            height: 0px;
            border-left: 20px red solid;
            border-top: 20px yellow solid;
            border-right: 20px green solid;
            border-bottom: 20px pink solid;
        }
        /* 圆 */
        .inner2{
            border-radius: 50%;
            width: 100px;
            height: 100px;
            background-color: red;
        }
        /* 圆圈 */
        .inner3{
            border-radius: 50%;
            width:50px;
            height: 50px;
            border: 20px solid red;
        }
        /* 缺扇形圆 */
        .inner4{
            border-radius: 50%;
            width: 50px;
            height: 50px;
            border: 20px solid red;
            border-left: 20px solid transparent;
        }
    </style>
</head>
<body>
    <div class="box">123</div>
    <div class="inner1"></div>
    <div class="inner2"></div>
    <div class="inner3"></div>
    <div class="inner4"></div>
</body>
</html>